Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 6 Oct 2022 11:56:51 +0200 | Subject | Re: [PATCH v2 1/1] sched/fair: Check if prev_cpu has highest spare cap in feec() |
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On Thu, 6 Oct 2022 at 10:11, Pierre Gondois <pierre.gondois@arm.com> wrote: > > When evaluating the CPU candidates in the perf domain (pd) containing > the previously used CPU (prev_cpu), find_energy_efficient_cpu() > evaluates the energy of the pd: > - without the task (base_energy) > - with the task placed on prev_cpu (if the task fits) > - with the task placed on the CPU with the highest spare capacity, > prev_cpu being excluded from this set > > If prev_cpu is already the CPU with the highest spare capacity, > max_spare_cap_cpu will be the CPU with the second highest spare > capacity. > > On an Arm64 Juno-r2, with a workload of 10 tasks at a 10% duty cycle, > when prev_cpu and max_spare_cap_cpu are both valid candidates, > prev_spare_cap > max_spare_cap at ~82%. > Thus the energy of the pd when placing the task on max_spare_cap_cpu > is computed with no possible positive outcome 82% most of the time. > > Do not consider max_spare_cap_cpu as a valid candidate if > prev_spare_cap > max_spare_cap. > > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
nit: the reviewed tag should be after the signed-off
> Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> --- > kernel/sched/fair.c | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 914096c5b1ae..bcae7bdd5582 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6900,7 +6900,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > for (; pd; pd = pd->next) { > unsigned long cpu_cap, cpu_thermal_cap, util; > unsigned long cur_delta, max_spare_cap = 0; > - bool compute_prev_delta = false; > + unsigned long prev_spare_cap = 0; > int max_spare_cap_cpu = -1; > unsigned long base_energy; > > @@ -6944,18 +6944,19 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > if (cpu == prev_cpu) { > /* Always use prev_cpu as a candidate. */ > - compute_prev_delta = true; > + prev_spare_cap = cpu_cap; > } else if (cpu_cap > max_spare_cap) { > /* > * Find the CPU with the maximum spare capacity > - * in the performance domain. > + * among the remaining CPUs in the performance > + * domain. > */ > max_spare_cap = cpu_cap; > max_spare_cap_cpu = cpu; > } > } > > - if (max_spare_cap_cpu < 0 && !compute_prev_delta) > + if (max_spare_cap_cpu < 0 && prev_spare_cap == 0) > continue; > > eenv_pd_busy_time(&eenv, cpus, p); > @@ -6963,7 +6964,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > base_energy = compute_energy(&eenv, pd, cpus, p, -1); > > /* Evaluate the energy impact of using prev_cpu. */ > - if (compute_prev_delta) { > + if (prev_spare_cap > 0) { > prev_delta = compute_energy(&eenv, pd, cpus, p, > prev_cpu); > /* CPU utilization has changed */ > @@ -6974,7 +6975,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > } > > /* Evaluate the energy impact of using max_spare_cap_cpu. */ > - if (max_spare_cap_cpu >= 0) { > + if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) { > cur_delta = compute_energy(&eenv, pd, cpus, p, > max_spare_cap_cpu); > /* CPU utilization has changed */ > -- > 2.25.1 >
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